1. Field of the Invention
The present relates to hydrogen absorbing Ni-based alloys and sealed rechargeable alkaline batteries or cells containing such alloys as an active material for their negative electrodes.
2. Description of Prior Art
Generally, sealed Ni-hydrogen rechargeable batteries include a negative electrode provided with a hydrogen absorbing alloy as an active material, an Ni positive electrode, a separator and an alkaline electrolyte. The hydrogen absorbing alloys constituting the negative electrode are desired to have the following characteristics, for example.
(a) They have high capability to absorb and release hydrogen. PA1 (b) They show a relatively low equilibrium hydrogen dissociation pressure (which corresponds to the plateau pressure on PCT curve at a temperature in the vicinity of room temperature) as low as not higher than 5 atm. PA1 (c) They exhibit high corrosion resistance and high durability or resistance to deterioration or aging. PA1 (d) They show high hydrogen oxidizing capability (or catalytic activity). PA1 (e) They are hardly converted to fine powder when absorption and release of hydrogen are repeated. PA1 (f) They cause no or less environmental pollution. PA1 (g) Their cost is low. PA1 (ii) A hydrogen absorbing Ni-based alloy consisting of 5 to 20% by weight of Ti, 10 to 37% by weight of Zr, 4 to 18% by weight of Mn, 0.1 to 10% by weight of V, 0.01 to 5% by weight of Fe, 0.01 to 3.5% by weight of Al, 0.05 to 6% by weight of Cr, and balance Ni and unavoidable impurities. PA1 (iii) A hydrogen absorbing Ni-based alloy consisting of 5 to 20% by weight of Ti, 10 to 37% by weight of Zr, 4 to 18% by weight of Mn, 0.1 to 10% by weight of V, 0.01 to 5% by weight of Fe, 0.01 to 3.5% by weight of Al, 0.1 to 7% by weight of Cu and balance Ni and unavoidable impurities. PA1 (iv) A hydrogen absorbing Ni-based alloy consisting of 5 to 20% by weight of Ti, 10 to 37% by weight of Zr, 4 to 18% by weight of Mn, 0.1 to 10% by weight of V, 0.01 to 5% by weight of Fe, 0.01 to 3.5% by weight of Al, 0.1 to 7% by weight of Cu, 0.05 to 6% by weight of Cr, and balance Ni and unavoidable impurities. PA1 (v) A hydrogen absorbing Ni-based alloy consisting of 5 to 25% by weight of Ti, 10 to 37% by weight of Zr, 4 to 20% by weight of Mn, 0.1 to 10% by weight of V, 0.01 to 5% by weight of Fe, 0.01 to 4.5% by weight of Al, 0.01 to 13% by weight of W, and balance Ni and unavoidable impurities. PA1 (vi) A hydrogen absorbing Ni-based alloy consisting of 5 to 25% by weight of Ti, 10 to 37% by weight of Zr, 4 to 20% by weight of Mn, 0.1 to 10% by weight of V, 0.01 to 5% by weight of Fe, 0.01 to 4.5% by weight of Al, 0.05 to 6% by weight of Cr, 0.01 to 13% by weight of W, and balance Ni and unavoidable impurities. PA1 (vii) A hydrogen absorbing Ni-based alloy consisting of 5 to 25% by weight of Ti, 10 to 37% by weight of Zr, 4 to 20% by weight of Mn, 0.1 to 10% by weight of V, 0.01 to 5% by weight of Fe, 0.01 to 4.5% by weight of Al, 0.1 to 7% by weight of Cu, 0.01 to 13% by weight of W, and balance Ni and unavoidable impurities. PA1 (viii) A hydrogen absorbing Ni-based alloy consisting of 5 to 25% by weight of Ti, 10 to 37% by weight of Zr, 4 to 20% by weight of Mn, 0.1 to 10% by weight of V, 0.01 to 5% by weight of Fe, 0.01 to 4.5% by weight of Al, 0.1 to 7% by weight of Cu, 0.05 to 6% by weight of Cr, 0.01 to 13% by weight of W, and balance Ni and unavoidable impurities. PA1 (ix) A hydrogen absorbing Ni-based alloy consisting of 10.1 to 13.9% by weight (13 to 18 atomic %) of Ti, 22.3 to 29.4% by weight (15 to 20 atomic %) of Zr, 8.9 to 13.3% by weight (10 to 15 atomic %) of Mn, 4.1 to 9.9% by weight (5 to 12 atomic %) of V, 3.1 to 6.1% by weight (3 to 6 atomic %) of Cu, 0.1 to 2.7% by weight in total of Fe and Al provided that Fe and Al are present in amounts not smaller than 0.01% by weight, respectively, and balance Ni and unavoidable impurities. PA1 (x) A hydrogen absorbing Ni-based alloy consisting of 10.1 to 13.9% by weight (13 to 18 atomic %) of Ti, 22.3 to 29.4% by weight (15 to 20 atomic %) of Zr, 8.9 to 13.3% by weight (10 to 15 atomic %) of Mn, 4.1 to 9.9% by weight (5 to 12 atomic %) of V, 3.1 to 6.1% by weight (3 to 6 atomic %) of Cu, 0.1 to 2.7% by weight in total of Fe, Al and Cr provided that Fe and Al are present in amounts not smaller than 0.01% by weight, respectively, and that Cr is present in an amount not smaller than 0.05% by weight, and balance Ni and unavoidable impurities.
As is well known in the art, sealed Ni-hydrogen rechargeable batteries using as an active material such hydrogen absorbing alloy as having the above-listed characteristics could exhibit various desirable characteristics such as large discharge capability, long lifetime of repeated cycle of charging and discharging, excellent rapid charging and discharging characteristics, and low self-discharge.
Therefore, research and development have been made increasingly on hydrogen absorbing alloys suitable for use as an active material in batteries, particularly sealed Ni-hydrogen rechargeable batteries and various hydrogen absorbing alloys have been proposed as described, for example, in JP-A-61-45563 and JP-A-60-241652.
However, none of the hydrogen absorbing alloys thus far proposed does always satisfy all the characteristics required for as the active material for the negative electrodes in sealed Ni-hydrogen rechargeable batteries, and therefore further development is now desired.